Sliding mode control of a tokamak transformer

A novel inductive control system for a tokamak transformer is described. The system uses the flux change provided by the transformer primary coil to control either the electric current or the internal inductance of the transformer´s secondary plasma circuit load. The internal inductance control is used to regulate the slow flux penetration due to the skin effect, providing first-order control over the shape of the plasma current density profile in the highly conductive plasma. Inferred loop voltages at specific locations inside the plasma are included in a state feedback structure to improve controller performance. Experimental tests have shown that the plasma internal inductance can be controlled inductively for a whole pulse starting just 30ms after the beginning of plasma breakdown. The details of the control system design are presented, including the transformer model, observer algorithms and controller design.